1. Field of Use
The invention relates to the use of polyacrylamide friction reducers and more particularly to the use of selected peroxides to break down the viscosity of the polyacrylamide friction reducers when friction reduction is no longer required.
2. Related Art
In the petroleum industry it is an increasingly common practice to perform a procedure known as a slickwater fracturing. This is a method of stimulating the production of hydrocarbons from a well by pumping water at high rates into the well, thus creating a fracture in the productive formation. Practical and cost considerations for these treatments require the use of materials to reduce pumping pressure by reducing the frictional drag of the water against the well tubulars. Polyacrylamide polymers are very widely used for this purpose.
One ongoing problem with the use of these polymers is their persistence. A large fraction of the polyacrylamide used in a slickwater treatment frequently stays within the producing formation. This has several ill effects on the desired goal of stimulating production: the polymer residue may actually plug some of the permeability of the rock; it may hinder recovery of the water used in the fracturing treatment; and it provides a source of nitrogen that can support the growth of bacteria in the well. Polyacrylamide that is not absorbed but that remains in solution in recovered water will also make disposal of that water more difficult.
A number of strategies have been used to deal with this problem. Chatterji in U.S. Pat. No. 4,144,179 teaches the use of organic peroxides in connection with a reducing agent in order to break up a well treatment fluid containing an organic gelling agent. Dawson in U.S. Pat. No. 6,983,801 teaches the use of esters and/or crosslinkers in connection with a breaking agent to break down the viscosity of a hydratable polymer in a well treating fluid. However, there is still a need for a viscosity breaker for a well treatment fluid that contains a polyacrylamide friction reducer.